Conventional microwave mechanical, electro-mechanical, and electronic switches may not compatible with on-chip integration with, and cryogenic operation of superconducting electronic circuits, because of incompatible fabrication processes and high power dissipation. Likewise, tunable filters that are commonly realized by use of either active components such as voltage-variable capacitors i.e. varactors, mechanical drivers, or ferroelectric and ferrite materials, are not easily controllable by signal levels that can be generated with single flux quantum (SFQ) technologies, and many are not operable at cryogenic temperatures. While superconducting microwave filters, both fixed and tunable, have been previously realized using both high temperature and low temperature superconductors, their use in switching applications suffered from high return loss, limited usable bandwidth, and poor out-of-band off-state isolation.
Semiconductor cross-bar switches, both for digital and microwave signals, are in wide use in reconfigurable signal routing applications such as switch matrices, transceivers, and test and communications systems. The cross-bar switch is a 4-port device, where in a first setting (referred to as ‘Bar state’) a first input port is connected to a first output port and a second input port is connected to a second output port, and in a second setting (referred to as ‘Cross state’) the first input port is connected to the second output port and the second input port is connected to the first output port. However, conventional cross-bar switches are generally not compatible with cryogenic ultra-low-power consumption applications and in general require voltage control signals of order of a few volts which are incompatible with SFQ control technologies.